Summary The Bell 204B helicopter (registration C-GRGY, serial number2022), operated by Gateway Helicopters Ltd., was conducting a survey job at Marathon, Ontario, with a crew comprising a pilot and an aircraft maintenance engineer. They departed Marathon on the day of the occurrence at about 0900 eastern daylight time to return to Sudbury, Ontario, flew to Wawa, Ontario, for fuel, and continued to Sudbury. The helicopter was on final approach to Sudbury Airport at about 1145 with the wind from the south-southwest at less than five knots. When the collective was raised and the cyclic pulled aft to reduce the sink rate and airspeed, the helicopter yawed to the right, and the pilot was unable to correct with left pedal. The collective was lowered and the cyclic pushed forward to increase the airspeed. The helicopter returned to a normal flight condition at 60KIAS (knots indicated airspeed), and the pedals were neutral. The pilot aborted the approach and flew a left-hand downwind approach for Runway22. During the second approach, when the collective was raised to slow the sink rate, there was a thump and the left pedal went to full deflection. The pilot declared an emergency then flew several circuits to determine the best way to make a landing. The helicopter flew well at 40KIAS, and the heading could be controlled by adjusting the throttle. The helicopter was lined up with the runway about two miles back on a shallow approach and crossed the runway threshold at a height of three to five feet and about 40KIAS. It touched down gently at approximately 30KIAS with 80percent rotor rpm and skidded about 90feet before coming to a stop. There were no injuries. Ce rapport est galement disponible en franais. Other Factual Information At the time of the occurrence, about 1145 eastern daylight time,1 the weather was good and not considered to be a factor. The pilot-in-command (PIC) was seated in the right seat. He held a valid commercial helicopter pilot licence. As of July2005, the PIChad accumulated approximately 3600total flying hours and 300hours on type. The aircraft maintenance engineer (AME) was properly licensed and had worked in the helicopter industry for two years as an apprentice and three years as a licensed AME. The AMEspent his first years working on small helicopters such as the RobinsonR22 and R44,and the Bell206. In the fall of 2002,he moved up to a medium helicopter, the Bell205. Gateway Helicopters Ltd. hired the AME in March2004, to work on its Bell204B, which is similar to the Bell205. During the busy season, helicopter companies typically assign a crew consisting of a pilot and an AMEto a helicopter. The crew work and fly together wherever the helicopter might be sent or stationed. When the crew is scheduled for time off, another crew is assigned to the helicopter. On checking the helicopter after the flight, it was discovered that a cable to the tail rotor pitch change mechanism had come undone. Investigation by the company showed that the cable had come undone at one of the two speed rigs,2 and that the threaded end of the speed rig had not been lock wired. Additionally, it was found that the threaded end of the other speed rig had also not been lock wired (see Photo1). In December 2004, the helicopter was removed from service for repainting and a tailboom change. The AME involved in the occurrence flight removed the pitch control chain and tail rotor assembly, but did not remove the cables or speed rig assemblies that were transferred to the replacement tail boom. He completed the reassembly with the aid of two other engineers and two apprentices. Following the reassembly, the AME rigged and lock wired the tail rotor controls. Because the other two engineers were not experienced on this type of helicopter, the AME had the pilot perform the independent inspection. The aircraft was released into service in February2005. The helicopter was flown approximately 270 hours over the next few months. During this time, two 100-hour inspections were completed, which included an Airworthiness Directive (AD) CF90-06 PartA (PartA) inspection. One additional PartA inspection was carried out following a sprocket change on the pitch change mechanism. A PartA inspection calls for removing, inspecting, and reinstalling the chain to the tail rotor pitch change mechanism every 100hours. Additionally, an ADCF90-06 PartB (PartB) inspection requires a detailed visual inspection of the chain every 25hours. A PartB inspection was conducted eight times before the occurrence. The chain drives the pitch change mechanism and is attached to the tail rotor pitch change cables by the speed rigs. During the subsequent PartA inspections, the speed rigs were lock wired the same way that they had been found. Six hours before the occurrence, a 50-hour inspection was carried out, which included a PartB inspection. As a precaution, the AME also checked the cable tension. With the exception of one PartA inspection and two PartB inspections, all other PartA and Binspections were performed by the occurrence AME, and the speed rig lock wiring was independently checked by the occurrence pilot. The investigation found that, following the initial tail-boom installation, the AME followed the procedures in the maintenance manual, but only lock wired the quick disconnect and not the threaded portion of the speed rig. The last part of the instructions states, "Lockwire the speed rigs as shown in figure7-32. Check complete tail rotor pitch control system for security, safetying and freedom of operation." The maintenance manual instructions were reviewed and found to provide adequate guidance for the task. A properly lock-wired speed rig will have one piece of lock wire securing the quick-disconnect ball end and another piece securing the threaded end (see Photo2). The error made in lock wiring was duplicated in the subsequent Part A inspections. As well, the investigation found that the hole where the lock wire goes through the speed rig on the threaded end was small and partially hidden by a spring. The use of control cables in the aviation industry is common practice, especially in older aircraft. While their use is more common in fixed-wing aircraft, where most or all of the flight controls use cables, they are also found in helicopters, although to a much lesser degree. Typically, their use in helicopters has been limited to control input to the tail rotor. Standard 571.10 of the Canadian Aviation Regulations requires that work that disturbs the engine or flight controls be inspected for correct assembly, locking, and sense of operation by at least two individuals, and that the technical record contain the signatures of both of them. To ensure that these critical systems are assembled correctly before flight, the person performing the independent inspection should be suitably trained and experienced on the type of aircraft. The independent inspection must be completed before the maintenance release. Although not part of the standard, Airworthiness Notice C0103 further explains the requirements and procedures for conducting independent inspections. The pilot had received basic training on independent control checks as part of his elementary maintenance training before the occurrence and met the requirements for completing the inspection. However, he did not detect the missing lock wire on the speed rig while carrying out the independent checks following the tail boom replacement and subsequent PartA inspections. During the investigation, it was determined that the company employees were knowledgeable in their respective fields and took their work seriously. It was equally evident that everyone took pride in their work and realized the importance of performing their work to the highest standard.